Nowadays, laminated films having an ethylene-vinyl alcohol copolymer layer have been used in applications such as packaging materials for food and medical applications, taking advantages of their superior gas barrier properties, stretchability, thermoformability and the like. Recently, for the purpose of improving various types of performances such as gas barrier properties, various multilayered structures have been proposed in which a plurality of resin-layers are laminated, each layer having a thickness of micron or submicron order.
Conventional multilayered structures developed so far in which a plurality of resin-layers of an ethylene-vinyl alcohol copolymer are laminated include, for example: (1) an elastomeric barrier film in which at least ten layers of a microlayer polymer composite formed from a fluid barrier material such as an ethylene-vinyl alcohol copolymer, and an elastomer material such as thermoplastic polyurethane are alternately laminated (see Japanese Unexamined Patent Application (Translation of PCT Application), Publication No. 2002-524317); (2) multilayer film alternately including layers of a hard polymer material such as an ethylene-vinyl alcohol copolymer and flexible polymer material (see Japanese Unexamined Patent Application (Translation of PCT Application), Publication No. 2003-512201), and the like.
However, according to the aforementioned conventional multilayered structure (1), adhesiveness between a fluid barrier material such as an ethylene-vinyl alcohol copolymer and an elastomer material such as thermoplastic polyurethane is not in any way considered. In addition, also according to the aforementioned conventional multilayered structure (2), the hard polymer material per se such as an ethylene-vinyl alcohol copolymer, and combination of the same with the flexible polymer material, and the like are not investigated in connection with the interlayer adhesiveness, but only a technique of strengthening the adhesiveness between each layer using a joining layer merely consisting of a hot melt adhesive is disclosed. Therefore, according to these conventional multilayered structure (1) and multilayered structure (2), the interlayer adhesiveness is insufficient, and due to delamination between layers and the like, cracks are likely to be generated on the barrier layer, whereby durability may be deteriorated. As a result, in the conventional multilayered structure (1), gas barrier properties may be insufficient for use in food packaging and the like.